1. Field of the Invention
The present invention relates to a method of and an apparatus for processing an image and, more particularly, to image processing method and apparatus in which coding and decoding of the image data are conducted on the basis of such blocks.
2. Description of the Related Art
Apparatus has been known in which image data read by an image reading device is delivered to an image output device such as a printer, e.g., a laser beam printer (LBP), which prints the image. In this type of apparatus, it is a common measure to temporarily store the read image data in an image memory when the image reading operation performed by the image reading device and the output operation by the image output device cannot be executed in real time. In order to improve the storage efficiency of the memory, it has been proposed to code the image data to be stored in the image memory so as to reduce the quantity of data, particularly when the quantity of the image data is large as is the case of color image data.
When the image data is to be enlarged or reduced, the enlarging or reducing operation is conducted in a batch manner before the coding of the image data or after decoding of the coded image data because enlargement or reduction of coded image data is very difficult to conduct.
Enlargement or reduction, conducted in a batch manner before coding or after decoding, poses a problem in that quantization errors due to coding or decoding are increased when the image is enlarged or reduced, especially in a case of using a non-reversible encoding method. For instance, when a reduction of image data is conducted prior to coding/decoding, the quantity of the image data is decreased so that quantization errors are increased.